1. Field of the Invention
The present invention relates to mechanisms for communicating information between semiconductor chips. More specifically, the present invention relates to a method and an apparatus for receiving and amplifying an input signal received from a capacitive sensor.
2. Related Art
Advances in semiconductor technology presently make it possible to integrate large-scale systems, including tens of millions of transistors, onto a single semiconductor chip. Integrating such large-scale systems onto a single semiconductor chip increases the speed at which such systems can operate, because signals between system components do not have to cross chip boundaries, and are not subject to lengthy chip-to-chip propagation delays. Moreover, integrating large-scale systems onto a single semiconductor chip significantly reduces production costs, because fewer semiconductor chips are required to perform a given computational task.
Unfortunately, integrating a large-scale system onto a single semiconductor chip greatly increases the data transfer rates required to communicate between semiconductor chips. Data is presently moved onto and off of a semiconductor chip through I/O pads located on the boundary of the semiconductor chip. Pin-grid array packaging technologies have increased the number of I/O pads available for this purpose. However, this increase has not kept pace with the exponential increase in the amount of circuitry that can be integrated onto a semiconductor chip.
Hence, as integration densities continue to increase, each I/O pin must satisfy I/O requirements for progressively larger amounts of on-chip circuitry. Furthermore, increasing integration densities allow higher clock on-chip speeds, and higher on-chip clock speeds mean that more clock cycles are required to move data from the interior of a semiconductor chip to the I/O pins on the border of the semiconductor chip.
Some researchers have begun to explore the possibility of using capacitive transmitters located on a first semiconductor chip to transmit signals to corresponding capacitive receivers located on the surface of a second semiconductor chip. This allows data to be transferred from directly from locations within the interior of the first semiconductor chip to locations within the interior of the second semiconductor chip without passing through I/O pins located on the chip boundaries. It also makes it possible to provide many more communication pathways between semiconductor chips because the signals do not have to be routed through a limited number of I/O pins.
However, the electrical signals received through a capacitive sensor are very weak, and must be greatly amplified in order to be used by circuitry within the semiconductor chip. This amplification process consumes a great amount of power because the amplification transistors must be kept very near their threshold levels in order to detect minute variations and input voltage. This power consumption is further multiplied if there exist large numbers of capacitive sensors.
Hence what is needed is a method and an apparatus for amplifying an input signal received from a capacitive sensor without consuming a large amount of power.
One embodiment of the present invention provides a system for amplifying an input signal received from a capacitive sensor. The system includes an input for receiving an input signal from the capacitive sensor and an amplifier that amplifies the input signal to produce an output signal. This amplifier includes a pull-up circuit that pulls the output signal up to a high voltage when the input signal exceeds a threshold voltage. It also includes a pull-down circuit that pulls the output signal down to a low voltage when the input signal falls below the threshold voltage. After the output signal is pulled up to the high voltage, the pull-up circuit enters a refractory state in which the pull-up circuit uses a limited current, and the pull-down circuit enters a receptive state in which the pull-down circuit is sensitized to react to small changes in the input signal. After the output signal is pulled down to the low voltage, the pull-down circuit enters a refractory state in which the pull-down circuit uses a limited current, and the pull-up circuit enters a receptive state in which the pull-up circuit is sensitized to react to small changes in the input signal.
In one embodiment of the present invention, the system includes an output delay chain that produces feedback from the output signal. After the output signal is pulled up to the high voltage, this feedback causes the pull-up circuit to enter the refractory state and causes the pull-down circuit to enter the receptive state. After the output signal is pulled down to the low voltage, this feedback causes the pull-down circuit to enter the refractory state and causes the pull-up circuit to enter the receptive state.
In one embodiment of the present invention, the system includes a bi-stable circuit. This bi-stable circuit is configured to hold the output to the high voltage until the input signal falls below the threshold voltage. It is also configured to hold the output to the low voltage until the input signal rises above the threshold voltage.
In one embodiment of the present invention, the system includes a pull-up current mirror with the pull-up circuit that is configured to limit the current used by the pull-up circuit while in the refractory state.
In one embodiment of the present invention, the system includes a pull-down current mirror with the pull-down circuit that is configured to limit the current used by the pull-down circuit while in the refractory state.
In one embodiment of the present invention, when the pull-down circuit is in the receptive state and the input voltage drops below the threshold voltage, the pull-down circuit is configured to enter an active state in which the pull-down circuit draws sufficient current to rapidly switch the output signal to the low voltage.
In one embodiment of the present invention, when the pull-up circuit is in the receptive state and the input voltage rises above the threshold voltage, the pull-up circuit is configured to enter an active state in which the pull-up circuit draws sufficient current to rapidly switch the output signal to the high voltage.
In one embodiment of the present invention, the system includes a high resting voltage circuit that is configured to generate a high resting voltage for the input when the pull-up circuit is in the refractory state.
In one embodiment of the present invention, the system includes a low resting voltage circuit that is configured to generate a low resting voltage for the input when the pull-down circuit is in the refractory state.
In one embodiment of the present invention, the capacitive sensor is an I/O pad on a surface of a semiconductor chip.